The present invention relates to the field of methods and arrangements that pertain to the monitoring of an object that is designed to emit a rotating or an oscillating beam; and relates more particularly to that part of this field in which the angular velocity of the beam is unknown.
It is sometimes desirable in a number of technical aspects to monitor an object that emits a rotating beam, by observing the movement of said beam. The object to be monitored may be a truck, a ship, an aircraft or part of a machine tool. The rotating beam is normally of an electromagnetic nature, for instance a narrow light cone, a laser beam or a narrow radar lobe emitted from a radar antenna.
WO, A1, 93/23764 describes a system for determining the position of an object. The object includes means for emitting a rotating laser beam. A number of sensors are placed at predetermined measuring positions around the object. Passage of the laser beam past the measuring positions is registered with the aid of the sensors. With knowledge of when the laser beam passes three of the measuring positions, the position of the object can be determined by means of a trigonometrical process.
One drawback with this system is that it is necessary to know the angular velocity of the rotating laser beam in order to determine the position of the object. The angular velocity of the beam is, however, not always known. For instance, the angular velocity may deviate from a standard angular velocity as a result of imperfections in the components that generate the beam, or the object may simply emit a rotating beam whose angular velocity is completely unknown.
The present invention is concerned with the monitoring of an object which is designed to emit a rotating or oscillating beam and whose angular velocity is unknown. In this respect, a main problem addressed by the invention is one of determining the angular velocity of the beam.
In brief, the problem is solved by iteratively producing on the basis of beam registration values that correspond to the unknown angular velocity to a successively increasing degree.
A primary object of the invention is to determine the angular velocity of the beam so that one may thereafter generate a final determination of the position of the object with a predetermined degree of accuracy. The invention provides both methods and arrangements to this end.
More specifically, the aforesaid problem is solved in the following manner. Those time points at which the beam passes a predetermined number of measuring positions are determined. An angular velocity start value is generated and a predetermined number (at least two) of object position determinations are made on the basis of the determined time points, the measuring positions and the start value. It is also determined whether or not the position determinations can be considered in sufficient agreement with one another, and if such agreement is found to exist the start value is accepted as an approximate value which approximates the angular velocity of the beam with acceptable accuracy. If the position determinations are not sufficiently in agreement, the start value is modified and new position determinations are made. This procedure is repeated for as many times as are necessary for the position determinations to be sufficiently in agreement, wherewith the start value is accepted as the approximate value of the angular velocity.
One main advantage afforded by the invention is that the position of the object can be determined without needing to know the angular velocity of the beam. A further advantage is that the invention does not only permit an object which emits rotating beams to be monitored, but also objects that emit xe2x80x9cscanningxe2x80x9d beams that perform an oscillatory reciprocating movementxe2x80x94roughly similar to a car windscreen wiper.
The invention will now be described in more detail with reference to preferred embodiments thereof and also with reference to the accompanying drawings.